The present invention relates to dye compositions used for colorimetric determination of a chemical or biochemical component (analyte) in an aqueous body fluid, such as blood. In particular the present invention relates to the field of dry reagent compositions for use on test strips adapted to receive a liquid sample of body fluid whereby the dye indicator composition wetted by the fluid reacts with the analyte and provides a visual or color indication of the presence or concentration of the analyte.
Indicator compositions for use in devices for color indication of various analytes in various body fluids are well known in the art and are embodied in numerous commercial products. Typically a dye composition or a dye couple composition is formulated in a solution which is applied to a test strip matrix then dried to form a dry chemistry system on the test strip. The dry chemistry system commonly involve an oxidizable dye or dye couple in combination with a oxidase or peroxidase specific to the analyte to be tested. The analyte reacts with the corresponding oxidase or peroxidase producing hydrogen peroxide which in turn oxidizes the dye or dye couple to produce the desired color change for indication of the presence or concentration of the analyte.
Example of such dye and dye couple systems are disclosed by Phillips et al. in U.S. Pat. Nos. 4,734,360; 5,059,394 and 5,304,468; by Yu in U.S. Pat. No. 5,453,360; Hoenes in U.S. Pat. No. 5,334,508 and by Hochstrasser in U.S. Pat. Nos. 3,964,871 and 4,059,407.
The disclosures of the above patents are incorporated herein by reference.
A number of the indicator systems disclosed in the above references are incorporated into various commercial products. While the products generally provide acceptable indication and testing under some conditions, certain problems exist with the prior dye systems. For example, in some dye systems the dry chemistry dye system existing on the test strip will allow the dye compounds to sublime from the test strip so that when the test strip is used by the consumer it may not provide an accurate indication. This limits the shelf life of the test strips. In some dye systems the color change provided by the dye system continues to change over time rather than reaching a stable end point. In those dye systems, the color indication must be accurately read at specific time intervals in order to obtain accurate indication of analyte presence or concentration. Some dye systems require a low pH to provide the necessary stability of the dye system. If the pH is below the desired pH level for stability of the enzymes used in the dye system the amount of enzymes used in the formulation must be increased. In such a case this can cause the enzymes to produce undesired indications due to the instability of the enzymes at the low pH required for the dye system.
In view of the above it is an object of this invention to provide an indicator dye system with improved stability to prevent sublimation of the dye system from the dry chemistry test strips.
It is an object of this invention to provide a dye system which will rapidly produce a stable end point thereby producing a final color indication in a short period of time thus eliminating the time dependent measurement or determination by the user.
It is a further object of this invention to provide a dye system which can be formulated and used a more normal pH to provide a more stable system for the enzymes present during the manufacture or use of the dye system.
The above objects as well as others are achieved by the compositions and systems of this invention as disclosed herein.
In one aspect this invention provides a dye composition comprising 3-methyl-6(M sulfonate)-benzothiazolinone-(2)-hydrazone (MBTH-S) where M is a positive ion providing a stable sulfonate salt and an oxidase enzyme or a peroxidase enzyme. This dye composition is formulated into a dry chemistry indicator system including other dye compounds to form dye couple system and conventional binders, chelating agents, buffers and the like, as known in the art. The MBTH-S is used in the composition in form of a stable sulfonate salt, of which the sodium salt is preferred, but the potassium, ammonium or other ionic form of the sulfonate salt may be used. In a preferred aspect of this invention the MBTH-S is used with another dye compound to form a dye couple for improved indication and a desired pH range in the range of about 6.
In another aspect this invention provides a device for testing a fluid for the presence or concentration of an analyte comprising a support for the dye composition wherein the dye composition comprises MBTH-S and an oxidase enzyme or a peroxidase enzyme as summarized above. The various mechanical configurations of such devices are known in the art and various configurations may be used incorporating the MBTH-S dye system of this invention adapted as desired for particular testing to be accomplished.
In another aspect this invention provides a method of testing a fluid for the presence or concentration of an analyte comprising contacting a fluid sample with a dry chemistry system comprising MBTH-S and an oxidase enzyme or a peroxidase enzyme as summarized above.